1. Technical Field of the Invention
The invention relates to decorative composite stone surfacing materials composed of a binder and decorative hard aggregates; more particularly it relates to a composite stone material made using a decorative hard aggregate composed of pieces of quartz or other materials of equal or greater hardness that have been coated with materials affecting the light reflection within the pieces.
2. Background Art
Composite stone refers to materials composed of a binder and appropriate stone or synthetic aggregates that when mixed together form a semi-liquid or paste consistency that can be applied to a floor or other substrate, or placed in a mold to make either flat, two dimensional plates for use as tiles or sheets, or three dimensional objects such as statues or blocks. The mixture is then cured by an appropriate method to a hardened, unfinished state as in cross section FIG. 1, and then the surface is ground to reveal the decorative qualities below the rough surface, as in cross section FIG. 2. Two dimensional tiles and sheets, and three dimensional objects, are widely produced in several areas of the world and are variously known as composite stone, agglomerated stone, manmade stone, polymer cement or terrazzo. The ratio of binder to aggregates commonly ranges from 5-50% binder to 50-95% aggregates, by volume.
The current technologies for producing composite or agglomerated stone utilize cements, epoxy, polyester, acrylic and other modern binders to hold the aggregates together in forming the composite stone. Methods of production range from simple mixing and molding to more advanced molding with vibration or molding using vacuum, vibration, and/or pressure techniques. Subsequently the binder is caused to harden by a method and time appropriate to the binder, and the resultant hardened composite stone can be further worked by grinding and polishing, to produce a visible surface with desired finish from rough ground to highly polished and glossy.
Whatever the method, the resulting composite stone has various looks and physical/chemical characteristics depending upon the choice of binder and aggregates. Various pigments, additives, fibers or other proprietary modifying components can be added to the mixture to achieve desired colors, manufacturing ability, cost reductions, or physical/chemical properties for the composite stone.
Terrazzo is an ancient form of composite stone, well known and widely utilized since Roman times. Originally most terrazzo was made from cement binder, marble and pigments. The mixture was spread on a substrate, hardened and ground. This method is still used today and is referred to as xe2x80x9cpoured-in-placexe2x80x9d terrazzo. The mixture can be applied to floors, walls, columns, furniture, stairs etc and then ground and polished after hardening. Such mixtures have also been placed in molds to form tiles, slabs, and blocksxe2x80x94which can be subsequently sliced into slabs or tiles for polishing. Composite stone stairs, containers, tabletops, furniture, statues and the like and are common, and are referred to as pre-fabricated, pre-cast or pre-formed terrazzo items.
In this century the cement has often been replaced with plastic binders such as epoxy, polyester, urethane, acrylic or other resins in order to improve characteristics of the finished composite stone material or to aid in production, as either poured-in-place or for pre-cast composite stones. Prior to this century and the advent of electric grinding machinery and modem grinding abrasives, the grinding and polishing was done by hand labor and therefore most of the aggregates were relatively soft such as marble, sea shells or glass. With the advent of electric grinding equipment and modem grinding abrasives harder aggregates such as granite and quartz are being used in the production of composite stone, both poured-in-place and pre-cast.
Over the last 40 years, up to about 10 years ago, the production of pre-cast composite stone was done with soft aggregates, which enabled it to be cast in the form of large blocks and then sliced into slabs nominally 0.3 to 4.0 cm in thickness; or as slabs and tiles, again typically in thickness from 0.3 to 4.0 cm, and in dimensions ranging from 12xc3x9712 inches up to 6xc3x9715 feet or larger. It wasn""t until recent improvements in diamond, cubic-borne nitride and silicon carbide and other grinding and polishing media that make calibrating, grinding, polishing and cutting of hard aggregates possible and cost effective.
The production and consumption of pre-cast tiles and slabs of composite stone, now about 100 million square feet per year, is a significant and growing part of the overall production of surfacings for floors, walls, exterior walls, counter tops, furniture, partitions and other architectural elements for the building construction industry. Producers of composite stones have devised various methods to provide improved or different appearances, and physical and chemical characteristics of these composite stones by using as the aggregate in the binder-aggregate mixture such materials as pieces of glass, mirror, plastic, and metal, in addition to the traditional aggregates of marble, granite, quartz, or other stones and minerals.
In general, composite stone can be divided into two groupsxe2x80x94hard and soft. xe2x80x9cHardxe2x80x9d composite stone contains aggregates and fillers such as quartz, granite, Aluminum Oxide or other minerals, natural or synthetic, with a Mohs hardness index (traditional, non-linear, scale of hardness where by definition talc=1, quartz=7 and diamond=10) of 6 or 7 and higher. xe2x80x9cSoftxe2x80x9d composite stones contain aggregates and fillers such as marble, glass, sea shells, plastic, metal with Mohs index typically less than 6 or 7. For context, consider that for marbles, glass, and the like, the Mohs index is usually in range of 3.0 to 5.5 or so.
The practical distinction is that in general, dirt and sand which comes into contact with such surfaces, whether the composite stone is used on the floor or on countertops, is composed largely of quartz, Mohs 7, that can easily scratch, abrade or destroy the surface of soft composite stones. Quartz is the most abundant mineral on the planet; and is a common component to dirt, dust, and grit in all parts of the world. Especially on walls and countertops and furniture having such decorative surfaces; abrasive agents used in many cleaning agents, knife edges, and other articles coming into contact with the surface, and of course the inevitable dirt, dust and grit, are sufficiently hard to scratch these Mohs 3-5 materials, causing accumulating damage and wear to such soft composite stone surfaces.
The following hard and soft composite stone materials are well known and commonly used in the industry, today. Their characteristics are described here giving the requisite usefulness from an aesthetic or durability point of view.
Group 1. Marble aggregatesxe2x80x94soft composite stonexe2x80x94marble has a hardness of 3-4 on Mohs scale and therefore is easy to grind and polish but also is also easily scratched when used on a floor or other area subject to abrasion. Marble is also absorbent and therefore easily stained and also subject to attach by even mild acids. Until about 1990, marble was the principle aggregate used in nearly all decorative composite stone production.
Group 2. Marble aggregates with addition of pieces of glass, mirror, metal, mother of pearl plastic, constitutes a soft composite stone. The glass, mirror or plastic can be colorless or colored and from clear/transparent to cloudy/nearly opaque. The metal or mother of pearl or soft (less than 7 Mohs) semi-precious stones come in many colors. The percentage of the added non-marble aggregates can be from a few percent as random dots on the surface, up to constituting most or all of the required aggregate in the composite stones aggregate-binder mixture. Products where the binder is a cement or plastic resin and the aggregate is partly, substantially, or wholly made from glass or mirror powder, granules or cullet have been produced by several firms for more than 10 years.
Group 3. Quartz, granite and other hard mineral aggregatesxe2x80x94hard composite stonexe2x80x94are now widely used as the aggregates in many types of composite stone because they have a Mohs hardness of 6 or higher and are highly resistant to abrasion and scratching, and are resistant to many chemicals, especially acids. In some cases the aggregate is quartz sand, without particular attention to aesthetic appeal, and the binder is a resin selected for exceptional chemical or heat resistance to make a composite stone material, referred sometimes as polymer cement, used for its thermal or chemical properties rather than decorative architectural application.
The use of glass chips in traditional poured-in-place terrazzo is well known in the industry for over 100 years. None the less, at least one recent patent attempts to distinguish the use of mirrors as a decorative aggregate material from the prior art. Martiny""s U.S. Pat. No. 5,445,880, COVERING WITH IMPROVED OPTICAL QUALITIES, issued Aug. 29, 1995, claims mirror-coated glass as a decorative component to a composite stone surfacing material. However, earlier patent art, LECHAT""s French Pat. No. 997,495, NEW AGGLOMERATE AND ITS MANUFACTURING PROCESS, published Jan. 7, 1952, notably not cited in Martiny""s U.S. case, speaks of pre-coating transparent particles or granules of aggregate with selected films, which after having an exposed side of a granule and its film covering opened by polishing of the decorative surface of the hardened agglomerate, light, as here translated from the French, xe2x80x9cpenetrates through the granules, is reflected on the opaque film, and passes back through the granules. . . xe2x80x9d According to LECHAT, as here translated, the transparent granules xe2x80x9cmay be made of glass, and consist, in this case, of broken bottle glass (green glass), broken window glass, gilded or silvered mirrors, etc., ground and size sorted or of any natural or synthetic transparent material, particularly methyl polymethacrylate, cellulose acetate, etc.xe2x80x9d
The weakness of all group 1 and 2 type soft composite stones is a combination of their relative softness and susceptibility to scratching and abrasion from common dust, dirt and grit, and to staining and chemical attach. Group 3 materials are less so, and this is the reason that many producers of composite stone have changed in the last 10 years or so to using the harder Group 3 quartz/granite class of aggregates for non-decorative purposes, specifically for better resistance to chemicals and to abrasion. The Martiny and Lechat disclosures refer to the use of glass and softer materials for decorative purposes, their disclosures claiming reflective properties through the polished facets of the coated particles, but fail to point out or anticipate in any way the relative benefits of expressly specifying harder versus softer decorative aggregate materials.
It is useful to consider that in their time, LECHAT and even MARTINY were likely unappreciative and unable to address the problem of durability/resistance to dirt of the decorative materials they described. The state of the art at those times with regard to composite stone materials was that soft (Mohs index less than 7) aggregates where the only materials used for decorative purposes. There are over 30 plants worldwide that have been producing marble composite stone for 20-30 years, with a total annual output of more than 150,000,000 square feet per year. The diamond and silicon carbide grinding media technologies necessary to produce hard aggregate composite stone materials did not exist in LECHAT""s time.
This explains why there is no awareness or discussion of the dirt hardness factor by either of these disclosures. Basically, until the 90""s, with the exception of GRANITECH in the late 80""s, the use of hard aggregates in composite stone was quite rare and new. It was just too difficult to make. LECHAT was clearly interested in glass and the then new plastics as decorative elements to his stone, without regard for the hardness and durability issues. This also explains generally why producers of otherwise hard aggregate (Mohs index of 6 or higher) composite stones, are adding glass, mirror, metal, plastic, or other soft (Mohs 3-7) decorative aggregates in order to improve the aesthetic appearance of the finished composite stone, at the expense of its durability.
In summary, the addition of glass, mirror, plastic or other soft aggregates to an otherwise potentially hard composite stone mixture for aesthetic appeal, makes the finished product more susceptible to abrasion and scratching, and therefore reduces the longevity and abrasion resistance of the overall composite stone surface. This is especially noticeable when the composite stone is used on floors or countertops subject to abrasion. In such cases the soft-aggregate pieces become dull, scratched or abraded away thus reducing the usefulness and value of the otherwise hard composite stone material.
For the purpose of describing and claiming the invention, a xe2x80x9chardxe2x80x9d material, mineral, compound, or aggregate is defined as one having a Mohs hardness index of at least seven (7), by definition equivalent to quartz. While scientists do use other scales for quantifying absolute hardness, quartz is the common material in much dirt which a durable composite stone must withstand, is a defining standard of the Mohs scale, and the Mohs scale is familiar to those skilled in the art, so this traditional standard is appropriate for this disclosure.
The word xe2x80x9ctransparentxe2x80x9d, when used herein without other qualification or context, means having some visible degree of transparency ranging from clear to translucent to nearly opaque, but short of being fully opaque.
It is an object of the current invention to provide a decorative composite stone material and method that produces a finished product, the decorative face of which is more durable and requires less maintenance, at less cost, than previous products. It is a further object to provide hard aggregates of enhanced aesthetic appeal for use in decorative, hard-aggregate composite stones. Specifically, the invention consists in providing as a decorative component of the aggregate, pieces of quartz, or other transparent material having a Mohs index of at least 7, whether naturally occurring or synthetic, in sizes from 0.001 mm to 25 mm diameter, which are coated with metal, ceramic, plastic or other material in such a way as to produce a coated particle which, when one side of a granule is ground and polished to expose an uncoated facet or window through which light passes into and out of granule, reflected off the coating on the unexposed portions of the granule, it provides reflective, colored, or reflective and colored properties. When incorporated into a hard-aggregate composite stone, these pieces of coated quartz or other hard aggregate add color, sparkle, glitter, metallic or other visual effect to the hard composite stone surface after grinding and polishing, without compromising the hardness and durability of the product.
The pieces of quartz so coated can be quartz which is entirely transparent; partly transparent or slightly milky; or nearly opaque, typically being either opaque white, tan, or other naturally occurring or synthetic quartz color. The color and transparency of the basic quartz, when combined with the various named coatings, creates a wide range of color-aesthetic particles or elements which can be incorporated into the hard-aggregate composite stone thereby providing an enhanced visual effect in the composite stone while maintaining the high abrasion and chemical resistance of the overall composite stone. Also, the sizes of the pieces of coated quartz, ranging from 0.001 mm to 25 mm diameter, enable a wide range of visual effects in the composite stone.
A discovery core to the invention, stated in a conclusory manner, is that quartz, the most common mineral on earth, is the dividing line between high cost and low cost maintenance composite stone floors. Composite stone flooring made using traditional soft aggregates such as marble, quickly lose their luster and shine under the grind of quartz-ladened grit and dirt, requiring frequent and expensive maintenance to restore the original appearance. A quartz-hard aggregate composite stone floor is highly resistance to the same factors, and will require substantially less effort, translating to lower cost, to maintain its appearance.
Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein I have shown and described only a preferred embodiment of the invention, simply by way of illustration of the best mode contemplated by me on carrying out my invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention.